Power and Refrigeration Cascade System

ABSTRACT

The present invention relates generally to combined power and cooling generation systems, and, more particularly, to a combined power and refrigeration cascade system (“PARCS”) that includes an electric power system (PS) that produces both electric power and medium-to-high-grade waste heat that can be used for providing the cooling and power supply needs of data centers and the like.

RELATED APPLICATION

The present application claims priority to U.S. provisional patentapplication No. 60/954,346, filed on Aug. 7, 2007; all of the foregoingpatent-related document(s) are hereby incorporated by reference hereinin their respective entirety(ies).

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to combined power and coolinggeneration systems, and, more particularly, to a combined power andrefrigeration cascade system (“PARCS”) that includes an electric powersystem (PS) that produces both electric power and medium-to-high-gradewaste heat that can be used for providing the cooling and power supplyneeds of data centers and the like.

2. Description of Prior Art

On-site power generation systems using combustion engines (for example,gas turbines) or fuel cells allow much higher energy efficiency throughthe utilization of the prime mover's waste heat. Such systems have beenoffered in a variety of configurations involving combined heat and power(“CHP”), combined cooling and power (“CCP”) or combined cooling, heatand power (“CCHP”). In all these configurations, the basic distinctionis the mode of waste heat utilization, which is dictated by the type ofload(s) served by the system. An important factor in determining theeconomic effectiveness of these systems is the matching of their powerand thermal output to the time varying power and thermal demands of theload(s). Ideally, the power and thermal output (heating or cooing) of anon-site system should be fully utilized by the load at all times, whichoccurs very rarely except when the power and thermal (e.g., cooling)demands are strongly correlated, as they are in computer data centers.

CCP and CCHP systems typically use absorption chillers to utilize thewaste heat for cooling. The most common type is single-effect or doubleeffect LiBr—H₂O absorption systems (ABS), modified to operate with thelower temperature waste heat from the power system. A CCP systemcomprising a 30%-efficient power generation system driving an R134avapor compression (“VC”) water chiller (COP_(c)˜6) and a double-effectabsorption chiller (COP_(a)˜1.1) can achieve a fuel-based cooling COPhigher than 2.4 under typical water-cooled chiller operating conditions(5° C. evaporator/°35 C. condenser). It should be noted, however, thatLiBr—H₂O ABS use water as a refrigerant and cannot provide sub zero ° C.refrigeration, making such systems unsuitable for low-temperaturerefrigeration applications.

Systems comprising cascaded combinations of exhaust-driven ABS and VCcooling have been proposed in which the ABS acts as a heat rejectionsystem for a bottoming VC system (see U.S. Pat. Nos. 4,745,768 and4,869,069). While these systems offer the potential for providingefficient on-site low-temperature refrigeration, they still suffer frompossible temporal mismatching when operated in grid-independent mode toserve time-dependent loads (for example, space heating and cooling orsupermarket refrigeration).

Grid-independent operation offers several advantages, especially with DCpower sources like fuel cells and DC loads like computers. With gridindependence, in addition to avoiding the grid-connection costs andcompliance with grid regulations, it is possible to eliminate severalsteps of power conversion from DC to AC or vice versa, which account foras much as a 50% power loss in data center applications.

Description Of the Related Art Section Disclaimer: To the extent thatspecific publications are discussed above in this Description of theRelated Art Section, these discussions should not be taken as anadmission that the discussed publications (for example, publishedpatents) are prior art for patent law purposes. For example, some or allof the discussed publications may not be sufficiently early in time, maynot reflect subject matter developed early enough in time and/or may notbe sufficiently enabling so as to amount to prior art for patent lawpurposes. To the extent that specific publications are discussed abovein this Description of the Related Art Section, they are all herebyincorporated by reference into this document in their respectiveentirety(ies).

SUMMARY OF THE INVENTION

Accordingly, it would be useful and desirable for an on-site powergeneration system to be grid-independent (see DEFINITIONS section),especially to be grid-independent with good temporal matching, and evenmore especially to be grid-independent with good temporal matching undera condition of time dependent load(s). In addition it would be usefuland desirable for the on-site power generation system to be able toprovide combined power generation and refrigeration for loads in whichthe refrigeration loads are strongly correlated with the power needs, asthey are in computer data centers.

Various embodiments of the present invention may exhibit one or more ofthe following objects, features and/or advantages:

(i) increase energy efficiency in a power and/or cooling generationsystem;

(ii) an electric power system (PS) that produces both electric power andmedium-to-high-grade waste heat;

(iii) efficient use of waste heat for providing the cooling and powersupply needs of a load;

(iv) high energy efficiency power supply and cooling for data centers orother load(s) where the need for cooling is positively correlated withthe power consumption; and

(v) a PARCS with 30-50% energy savings relative to a conventional powersupply and cooling system.

According to an aspect of the present invention, a power andrefrigeration cascade system includes an electric power system, arefrigeration system, and an absortion system. The refrigeration systemis powered at least in part by the electric power system. Therefrigeration system is thermally coupled to a component, wherein thecomponent is the electric power system and/or a load powered by theelectric power system. The absorption system is thermally coupled to therefrigeration system and configured to remove heat rejected by therefrigeration system. The thermal coupling between the refrigerationsystem and the absorption system enables a refrigeration systemcondensing temperature of less than approximately twenty degreesCelsius.

According to a further aspect of the present invention, an on-site powergeneration system includes an electric power system and a refrigerationcascade system. The refrigeration cascade system is thermally coupled tothe electric power system. The refrigeration cascade system isconfigured to temporally match cooling needs of a load coupled to theelectric power system based on actual power supplied to the load.

According to a further aspect of the present invention, a refrigerationcascade system includes a refrigeration system and an absorption system.The refrigeration system is configured: (i) to be powered at least inpart by electricity; and (ii) to be thermally coupled to a load poweredby electricity. The absorption system thermally coupled to therefrigeration system and configured to remove heat rejected by therefrigeration system. The thermal coupling between the refrigerationsystem and the absorption system enables a refrigeration systemcondensing temperature and an absorption system evaporating temperaturewhich are within less than approximately ten degrees Celsius of eachother.

A datacenter power and cooling system includes an electric power system,a server rack, a refrigeration system and an absorption system. Theserver rack is powered by the electric power system. The refrigerationsystem is powered at least in part by the electric power system and isthermally coupled to the server rack to remove heat from it. Theabsorption system is thermally coupled to the refrigeration system andconfigured to remove heat rejected by the refrigeration system. Thethermal coupling between the refrigeration system and the absorptionsystem enables a refrigeration system condensing temperature of lessthan approximately twenty degrees Celsius.

According to a further aspect of the present invention, a method ofreducing energy consumption by a computer chip powered by a power sourceincludes several steps. At a first coupling step, the computer chip isthermally coupling to a refrigeration system. At a powering step, therefrigeration system is powered, at least in part, by the power source.At a second coupling step, the refrigeration system is thermallycoupling to an absorption system. The thermal coupling between therefrigeration system and the absorption system enables a refrigerationsystem condensing temperature and an absorption system evaporatingtemperature which are within less than approximately ten degrees Celsiusof each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood and appreciated byreading the following Detailed Description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a high-level energy flow diagram of a first embodiment of aPARCS according to the present invention.

FIG. 2 is a graphical illustration that illustrates a minimum waste heatutilization efficiency in an ABS generator according to an embodiment ofthe present invention.

FIG. 3 is a high level schematic that illustrates potential savings fromon-site “native” DC power supply.

FIG. 4 is a block diagram that illustrates a PARCS with distributed RSaccording to an embodiment of the present invention.

FIG. 5 is a graph showing the power allocation of the first embodimentPARCS.

FIG. 6 is a graph showing the evolution of active and passive powerdissipation in CMOS CPUs associated with the first embodiment PARCS.

FIG. 7 is a graph showing typical CMOS chip thermal characteristics ofthe first embodiment PARCS.

FIG. 8 is a graph showing exemplary primary energy savings due to thefirst embodiment PARCS, where θ=0.0, 0.5, and 1.0%/° C.

FIG. 9 is a graph comparing power demand, where θ=0.0, 0.5, and 1.0%/°C., between a conventional grid-supplied system and the first embodimentPARCS.

FIG. 10 is a graph comparing power demands, where θ=0.75%/° C., betweena conventional system and the first embodiment PARCS.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. As shown in FIG. 4, a first embodiment of anon-site combined Power And Refrigeration Cascade System (“PARCS”) 100according to the present invention includes: fuel supply 101; electricpower system (“PS”) 102; exhaust to abs system line 103; generator 104;abs component 106; valve 108; condenser 110; valve 112; valve 114;solution HX 116; pump 118; valve 120; absorber 122; valve 124;evaporator 126; chilled water return manifold assembly 128; condensers130; compressors 131; evaporators 132; server rack assembly 133; and DCpower to data center line 134. The PS is preferably a heat-engine-drivenelectric generator or a fuel cell, that produces both DC electric powerand medium-to-high-grade waste heat. The components are interconnectedas shown in FIG. 4 to make the PARCS system 100.

The electric power output of the PS, which could be DC, AC or acombination of the two, is split between: (i) DC power to data centerline 134 (which supplies an electric load in the form of server rackassembly 133); and (ii) a complementary portion supplied to anelectrically-driven refrigeration system (RS) 128, 130, 131, 132, 133.The RS hardware may take various forms, now known or to developed in thefuture, such as, vapor-compression (VC), reversed Brayton (RB), reversedStirling (RS), thermoelectric (TE), magneto caloric (MC), or other typesof refrigeration systems. The heat rejected by the RS is pumped toambient air by means of an absorption heat pump system (ABS) 104, 106,108, 110, 112, 114, 116, 118, 120, 122, 124, 126. The ABS is activatedby the exhaust heat from the power system over line 103.

The ABS condenser 110 and absorber 122 could be either water-cooled orair cooled (water-cooled is preferred because of its higher efficiencyand compactness). In this fashion, the ABS and the RS subsystems arethermally integrated in a high-efficiency thermo-mechanical (e.g.,ABS/VC) or thermoelectric (e.g., ABS/TE) cascade. In this embodiment,the RS is depicted as a VC system (VCS).

As shown in FIG. 1, η is the thermal efficiency of the PS, λ is thefraction of its waste heat that is not recoverable (e.g., radiationloss), ξ is the waste heat utilization efficiency in the ABS generator,and φ is the fraction of the PS output needed to drive the RS. Thecoefficient of performance (COP) of the ABS based on its generator heatinput is COP_(a) and that of the RS based on its work input is COP_(r).The COP of the RS depends on its cold- and warm-side temperatures (theevaporator and condenser saturation temperatures in the VCS). In thePARCS of an embodiment of the present invention, the heat rejectiontemperature of the RS is dictated by the evaporator temperature of theABS, which, for LiBr—H₂O systems, is typically in the 5-10° C range.

In accordance with an embodiment of the present invention, for a datacenter application, the refrigeration system may be either centralizedand integrated with the ABS using a combined condenser/evaporator, ordistributed, with one (or more) RS per computer rack. The heat rejectedfrom the distributed RS units is transferred to chilled waterdistributed from a central waste-heat driven ABS. The RS and the ABScould be coupled in one of at least two ways: (i) in the centralizedconfiguration, an integrated condenser/evaporator heat exchanger ofsuperb effectiveness allows the condensing temperature in the VCS to beonly a few degrees higher than the evaporating temperature in the ABS.The VCS evaporator chills a heat transfer fluid (anti-freeze) that isdistributed to liquid-cooled rack cabinets; or (ii) in the distributedconfiguration, the ABS chilled water is delivered via a supply manifoldto the VCS condenser in each computer rack, and returned to the ABSevaporator (water chiller) via a return manifold. The VCS evaporator inthe rack is used either to chill air that cools the electroniccomponents in the rack, or to cool the electronic components directly.

In accordance with an embodiment of the present invention, in both ofthe configurations described herein, the condensing temperature of theVCS could be maintained herein 15° C., compared with the 35° C. typicalof water-cooled conventional VCS. As a result, the COP_(r) of the RS issubstantially higher than that of a conventional VCS. The lower RScondensing temperature in the PARCS of an embodiment of the presentinvention also enables lower temperature refrigeration with lessdeterioration in capacity and COP_(r) compared with a conventional VCS.This is one of the main advantages of the PARCS of an embodiment of thepresent invention. This advantage may also obviate the need for 2-stageVC and liquid injection to moderate the compressor discharge temperaturein low-temperature refrigeration, where high compression pressure ratiosare experienced (Liquid injection degrades refrigeration performance).

In accordance with an embodiment of the present invention, an importantadvantage of the PARCS of an embodiment of the present invention is itssuitability for computer data centers. In data center applications thepower consumption is dominated by computer needs (DC power), and therefrigeration load is nearly equal to computer power dissipation.Therefore, referring to the notation in FIG. 1:

Q_(r)˜W,

φCOP _(r)˜1−φ,

φ˜1/(1+COP _(r)),  Eq. (1)

where Q_(r) is the refrigeration load, and W is the computer powerconsumption. The performance of the RS in this case also depends on thatof the waste-heat-driven ABS, whose evaporator acts as the heatrejection means for the RS. For the data center application, the RS heatrejection temperature and rate are tied to the ABS evaporatortemperature and capacity, viz;

φη(1+COP _(r))=ξ(1−λ)(1−η)COP _(a),  Eq. (2)

For given values of ξ, λ, COP_(a), and COP_(r), Eq. (2) implies that,for a grid-independent PARCS of an embodiment of the present invention,φ should not exceed a limiting value, φ*, given by:

φ*=ξ(1−λ)((1−η)COP _(a)/[η(1+COP _(r))]≧φ.  Eq. (3)

This relationship highlights the importance of matching the PS, ABS andRS in stand-alone, grid-independent PARCS applications of an embodimentof the present invention. In the case of a data center where Eq. (1)applies, the combination of Eq. (3) with Eq. (1), yields the conditionfor the PARCS to match both the power and refrigeration needs of thedata center, namely:

ξ(1−λ)((1−η)COP _(a)/η≧1,  (Eq. (4)

which depends entirely on the PS and ABS characteristics, but, notably,not on those of the RS. The product of ξ and (1−λ) represents an overallwaste heat utilization efficiency, ξ. Thus, Eq. (4) may be written as:

ξ((1−η)COP _(a)/η≧1,  Eq. (4a)

In accordance with an embodiment of the present invention, thisrelationship, as described herein, is illustrated in FIG. 2. FIG. 2shows the minimum value of ξ that satisfies the constraint implied byEq. (4) for typical single-effect and double-effect ABS COP_(a). It canbe seen that higher waste heat utilization efficiencies are required inorder to satisfy the matching constraint (Eq. 4a) when a higherefficiency PS is employed. These conditions favor power generationsystems with a higher-temperature waste heat, such as gas turbines, ormolten-carbonate or solid-oxide fuel cells. A high waste heatutilization efficiency could also be achieved with medium-temperaturewaste heat if it is mostly in latent form (for example, extracted from acondensing PS exhaust effluent). It is also evident that single-effectABS cannot satisfy the data center matching constraint when a higherefficiency PS is employed (η>0.35). FIG. 4, as discussed in furtherdetail herein, also indicates that the matching constraint can be moreeasily satisfied with double-effect ABS, even for higher-efficiency PS(for example, medium- and high-temperature fuel cells).

In accordance with an embodiment of the present invention, η and λdepend on the type of the PS selected, and ξ and COP_(a) depend on thetype of the ABS that is compatible with the temperature and quality ofthe selected PS waste heat. For example, a PS whose waste heat that isat 100° C. or lower would be compatible with a single-effect ABS with atypical COP_(a) of about 0.6, whereas a PS whose waste heat that isavailable at 125° C. or higher would be compatible with a double-effectABS with a typical COP_(a) higher than 1.0. Generally, the higher thetemperature at which the PS waste heat is available, the higher theCOP_(a) of the ABS and the waste heat utilization efficiency (for agiven ABS cycle).

In accordance with an embodiment of the present invention, anotherimportant aspect of the PARCS of an embodiment of the present inventionwhen used with data centers, is its ability to generate “native” DCpower, possibly at several voltages suitable for powering computersystems. This has the potential substantially to reduce power conversionand conditioning losses. Conventional grid-powered systems coulddissipate close to 50% of their AC power input in the multiplerectifier/inverter/power-conditioning stages required for a data center.This advantage is especially present when a fuel cell is used as the PS,but could be obtained also with a thermo-mechanical (e.g., a combustionengine) PS driving DC electric generators. This is highlighted in FIG.3, which shows the various stages of AC/DC power conversion that can beeither eliminated or made more efficient by using an on-site DC powersupply as disclosed here. The overall efficiency of this subsystem couldbe increased from ˜50% value typical of grid-supplied equipment tobetter than 70% if native DC power is available on-site.

In accordance with an embodiment of the present invention, FIG. 4 showsa preferred embodiment of PARCS with distributed RS in further detail.FIG. 4 includes a fuel cell PS, distributed single-stage refrigerationsystems (one per rack), and a waste-heat driven water-cooleddouble-effect LiBr—H₂O ABS providing chilled water to cool thecondensers of the distributed VC RS. The fuel cell is of the medium- orhigh-temperature type (for example, phosphoric acid formedium-temperature, or molten-carbonate or solid-oxide forhigh-temperature). Although FIG. 4 shows VC RS, a reversed Stirling, TEor MC RS could also be used.

In accordance with an embodiment of the present invention, to illustratethe performance advantage of the disclosed PARCS of an embodiment of thepresent invention for data center applications, a PARCS similar to theone shown in FIG. 4 was analyzed. The RS capacity (central ordistributed) is matched to the cooling demands of the data center. FIG.5 shows the fraction of the PS output diverted to the VCS (FIG. 1) forcooling a data center over a range of evaporator temperatures from 10°C. (typical for air-conditioning), down to −40° C. (typical forlow-temperature refrigeration in supermarkets). The PS is assumed to bea fuel cell with a thermal efficiency of 40% and a waste heattemperature of ˜150° C. (˜300° F.). Because the fuel cell's nativeoutput is DC, it is possible to reduce the data center power demand byas much as 35% by eliminating the AC/DC conversions and voltagetransformers used in conventional grid-supplied data centers. The ABS isassumed to be a water-cooled double-effect LiBr—H₂O type operated at amoderate generator temperature (<100° C.) to achieve a thermal COP_(a)of 1.05 with heat rejection (absorber and condenser) at 35° C., and anevaporator saturation temperature of 10° C. Two lines are shown, onerepresenting matching the data center power demands (Eq. 1) and theother representing matching constrained by the capacity of thewaste-heat-driven ABS. As shown in FIG. 5, it is evident that the PARCSof an embodiment of the present invention is an excellent “match” over awide range of cold-side temperature for the type of correlated computingand refrigeration power demands presented by a data center.

In accordance with an embodiment of the present invention, as describedbelow, the PARCS of an embodiment of the present invention allowsefficient low temperature refrigeration. There are several advantages ofoperating computing hardware at lower temperature: higher reliability,potential for improved performance, and potential for reducing heatdissipation (See R. R. Schmidt and B. D. Notohardjono, High-End ServerLow-Temperature Cooling, IBM J. OF RES & DEV, vol 46, No. 6 (November2002)). For a given cooling scheme, the heat dissipation rate ofcomputer systems can depend both on the computing performance (forexample, clock rate) and operating temperature:

Q _(d) =F( P,T _(i)),  Eq. (5)

where Q_(d) is the computing power consumption at a computingperformance level P and internal temperature of the heat dissipatingcomponent, T_(i). This temperature is related to the coolanttemperature, T_(c), the cooling scheme, and the heat dissipation rate,Q_(d) through the familiar heat transfer equation:

Q _(d)=(T _(i) −T _(c))/R _(θ),  (Eq. (6)

in which R_(θ) represents the overall thermal resistance from the chipcore to the coolant, which depends on both the cooling scheme and theinternal thermal resistance of the electronic component (e.g., CPU die).

In accordance with an embodiment of the present invention, therelationship represented by Eq. (5) can be inferred from the powerdissipation characteristics of CMOS chips, which can be divided intoactive and passive components (the active component depends on the clockfrequency; the passive component is present even if the clock isstopped). Passive power dissipation has surpassed active powerdissipation in modern high-density, low voltage CMOS CPUs with lowthreshold voltage (as shown in FIG. 6). The active component is nearlyindependent of temperature, but the passive component, which isdominated by the dissipative effect of subthreshold leakage currents, isa strong function of temperature.

In accordance with an embodiment of the present invention, generally,active power can depend on clock frequency, f, and voltage, V:

Q_(a)=C_(a)V²f,  eq. (7)

and the leakage-dominated passive component to be of the form:

$\begin{matrix}{{Q_{p} = {C_{p}V\; {\exp \left( \frac{- {qV}_{th}}{k_{B}T_{i}} \right)}}},} & {{Eq}.\mspace{14mu} (8)}\end{matrix}$

where q is the electron charge, V_(th) is threshold voltage, and k_(B)is the Boltzmann constant. The total power dissipation from a CMOS chipcan thus be expressed as:

$\begin{matrix}{Q_{d} = {{C_{a}V^{2}f} + {C_{p}V\; {{\exp \left( \frac{- {qV}_{th}}{k_{B}T_{i}} \right)}.}}}} & {{Eq}.\mspace{14mu} (9)}\end{matrix}$

Equations (6) and (9) can be combined to yield an implicit expression ofthe form:

$\begin{matrix}{{Q_{d} = {{C_{a}V^{2}f} + {C_{p}V\; {\exp \left( \frac{- {qV}_{th}}{k_{B}\left( {T_{c} + {Q_{d}R_{\theta}}} \right)} \right)}}}},} & {{Eq}.\mspace{14mu} (10)}\end{matrix}$

which may be expressed explicitly as a function of f, V, and T_(c), withR_(θ) as a parameter:

Q _(d) =F(f,v,T _(c) ;R _(θ)).  Eq. (11)

In accordance with an embodiment of the present invention, the actualrelationship (Eq. 11) can be much more complex than the one derivedabove, but the relative trends can be examined by using the simple modelrepresented by Eq. (10), in which the clock frequency is used as asurrogate for the performance, P.

In accordance with an embodiment of the present invention, FIG. 7illustrates the relationship implied by Eq. (10) in normalized form.Charts of this qualitative nature can be produced for a chip, an entiremotherboard, a server, or a rack, for other performance metrics, andcooling schemes (R_(θ)). The iso-performance lines in FIG. 7 are onlymildly curved and may be treated as straight lines in simplifiedparametric analysis. Therefore, whether operating at a lower temperaturewould lead to a reduction in heat dissipation for a given computingperformance level and cooling scheme will depend on the parameter:

$\begin{matrix}{\theta = {\left( \frac{\partial{\overset{\_}{Q}}_{d}}{\partial T_{c}} \right)_{\overset{\_}{P},V,R_{\theta}}.}} & {{Eq}.\mspace{14mu} (12)}\end{matrix}$

It has been reported that that IBM's 750FX and 750GX processors exhibita 0.05 W/° C. and 0.1 W/° C. slopes, respectively. These translate intoθ values in the 0.5%/° C. to 1.0%/° C. range. (See D. Elson, 750X and750GX Power Dissipation Presentation, (Feb. 15, 2005). For thisanalysis, the effects of θ on PARCS performance of an embodiment of thepresent invention for three values of θ (0%, 0.5% and 1% per ° C.) areexamined, as discussed herein.

In accordance with an embodiment of the present invention, FIG. 8presents energy savings trends of the PARCS of an embodiment of thepresent invention relative to a conventional grid-supplied systemoperating with a 10° C. saturated evaporator temperature and 35° C.saturated condenser temperature, designated here as CS-10/35° C. Theoverall thermal efficiency of the grid-supplied power, including remotepower plant and transmission/distribution losses, was taken as 30%. Thesavings displayed in FIG. 9 does not include the potential savings fromthe use of on-site DC power supply in PARCS of an embodiment of thepresent invention. The PARCS of an embodiment of the present inventionprovides primary energy savings in excess of 33% compared with theCS-10/35° C. baseline, even if operated at the same 10/35° C. conditionsas CS-10/35° C. This is due to the higher thermal efficiency of the fuelcell power plant, and because of the utilization of the fuel cell'swaste heat in the ABS to lower the VCS condensing temperature.

In accordance with an embodiment of the present invention, FIG. 8 alsoshows the sensitivity of primary energy savings to θ. With a θ=0%, theprimary energy savings declines as the coolant temperature is lowered atthe same chip performance level, decreasing to less than 10% at −40° C.The savings is nearly flat for θ=0.5%/° C. and increases steadily toreach a value in excess of 50% at −40° C. for θ=1.0%/° C. Thisdemonstrates that newer, denser, lower voltage CMOS chips could benefitsignificantly from low temperature operation. The savings are evenhigher when account is made for the substantial energy savingsassociated with using the fuel cell's native DC output, as discussedherein.

In accordance with an embodiment of the present invention, FIG. 9displays the variation of the total power requirements (for dataprocessing and refrigeration), normalized with respect to the dataprocessing (IT) power demands of a conventional grid-connected systemcooled by a 10° C. evaporator. The power rating of the refrigerationequipment and the total power demand of the data center are considerablymore favorable with PARCS of an embodiment of the present inventioncompared with a conventional VCS at any low-side temperature. Thereduction in total power demand relative to CS-10/35° C. is evident downto −40° C. for θ=0.5% and 1.0%/° C., even without the advantage ofon-site DC power generation. This trend is also present, albeit to alesser extent, when the IT load is independent of operating temperature(i.e., θ=0.0%/° C.). Whereas the primary energy savings of PARCS of anembodiment of the present invention relative to CS-10/35° C. remainspositive over the entire range of evaporator temperatures from 10° C. to−40° C. (FIG. 8), PARCS' power demand is lower than that of CS-10/35° C.only down to about −10° C.

FIG. 10 compares the power demands of PARCS of an embodiment of thepresent invention relative to a conventional system, taking into accountthe advantage of on-site DC power generation. The grid-connected powersupply system shown in FIG. 3 has an overall efficiency of 48% whenoperated at conventional data center temperature. With a PARCS accordingto the present invention, the power conversion efficiency is raised to75% as a result of the elimination the various AC/DC conversion steps.The PARCS power conversion hardware is assumed to be maintained at thesame temperature as in a conventional data center. With PARCS of anembodiment of the present invention, a θ=0.75%/° C. It can be seen thatthe combined improvement due to DC power conversion, low temperatureoperation (−40° C.) and fuel-cell based cogeneration included in PARCSaccording to the present invention lead to a total power reduction inexcess of 50%. It should be noted that when these power reductions aretranslated into primary energy savings, PARCS of an embodiment of thepresent invention advantage over the conventional system rises to aneven more impressive 65%. This is because of the higher thermalefficiency of the fuel cell (40%) compared with grid power (30%).

In accordance with an embodiment of the present invention, the use ofPARCS of an embodiment of the present invention can result insubstantial reductions in primary energy consumption and power ratingsof power- and cooling-intensive applications such as data centers, andthe like. When multiple PARCS with appropriate spares are used, reliablegrid-independent operation can be achieved. When fuel cells are used inPARCS of an embodiment of the present invention, DC power can besupplied directly to the load at multiple voltages, eliminating themultiple energy-dissipating AC/DC electric power conversion andconditioning steps in a grid-connected power supply system. The primaryenergy savings potential of the DC power generation and the RS/ABScooling cascade afforded by a fuel-cell based PARCS could exceed 60%,even with low-temperature refrigeration. The benefits of the latter fordata centers include higher reliability, improved performance, enhancedability to handle the ever increasing heat fluxes produced by modemcomputer systems, for newer denser low voltage CMOS chips, and reductionin leakage power dissipation.

In accordance with a preferred embodiment of the present invention, thePARCS of an embodiment of the present invention is ideally suited todata centers, where the electric and refrigeration loads are steady andstrongly correlated. The matching parameter, φ, can be increased ordecreased by changing the VCS condenser/ABS evaporator temperature. Byraising this temperature, it is possible to lower the maximum generatortemperature and maximum solution concentration in the PARCS' ABS thanfor a conventional ABS unassisted by the cascade effect of the PARCS.This also results in a higher COP_(a) for the PARCS' ABS. The improvedconditions under which the ABS would work in PARCS of an embodiment ofthe present invention leads to a lower susceptibility to corrosion andcrystallization—two major risks in LiBr—H₂O absorption systems (the vastmajority of commercially-available ABS). With a lower RS condensingtemperature, lower initial cost and higher reliability would also berealized.

While PARCSs according to the present invention can be constructed fromcommercially-available phosphoric acid fuel cells, double effectLiBr—H₂O absorption chillers, and conventional vapor compressionrefrigeration systems, it can also be configured to operate with otherthermo-mechanical power generation systems such as gas turbines(micro-turbines) and gas engines, or with advanced high-temperature fuelcells (molten carbonate and solid oxide). It can also be configured withother RS such as Stirling, thermoelectric or magneto-caloric systems,and with other types of waste heat-activated heat pumps besides LiBr—H₂OABS (e.g., adsorption).

While several embodiments of the invention have been discussed, it willbe appreciated by those skilled in the art that various modificationsand variations of the present invention are possible. Such modificationsdo not depart from the spirit and scope of the invention.

DEFINITIONS

The following definitions are provided to facilitate claiminterpretation:

Present invention: means at least some embodiments of the presentinvention; references to various feature(s) of the “present invention”throughout this document do not mean that all claimed embodiments ormethods include the referenced feature(s).

Grid-independent: at least substantially grid-independent.

To the extent that the definitions provided above are consistent withordinary, plain, and accustomed meanings (as generally shown bydocuments such as dictionaries and/or technical lexicons), the abovedefinitions shall be considered supplemental in nature. To the extentthat the definitions provided above are inconsistent with ordinary,plain, and accustomed meanings (as generally shown by documents such asdictionaries and/or technical lexicons), the above definitions shallcontrol. If the definitions provided above are broader than theordinary, plain, and accustomed meanings in some aspect, then the abovedefinitions shall be considered to broaden the claim accordingly.

To the extent that a patentee may act as its own lexicographer underapplicable law, it is hereby further directed that all words appearingin the claims section, except for the above-defined words, shall take ontheir ordinary, plain, and accustomed meanings (as generally shown bydocuments such as dictionaries and/or technical lexicons), and shall notbe considered to be specially defined in this specification. In thesituation where a word or term used in the claims has more than onealternative ordinary, plain and accustomed meaning, the broadestdefinition that is consistent with technological feasibility and notdirectly inconsistent with the specification shall control.

Unless otherwise explicitly provided in the claim language, steps inmethod steps or process claims need only be performed in the same timeorder as the order the steps are recited in the claim only to the extentthat impossibility or extreme feasibility problems dictate that therecited step order (or portion of the recited step order) be used. Thisbroad interpretation with respect to step order is to be used regardlessof whether the alternative time ordering(s) of the claimed steps isparticularly mentioned or discussed in this document.

1. A power and refrigeration cascade system, comprising: an electricpower system; a refrigeration system powered at least in part by theelectric power system and thermally coupled to a component, wherein saidcomponent is selected from the group consisting of the electric powersystem and a load powered by the electric power system; and anabsorption system thermally coupled to the refrigeration system andconfigured to remove heat rejected by the refrigeration system, whereinthe thermal coupling between the refrigeration system and the absorptionsystem enables a refrigeration system condensing temperature of lessthan approximately twenty degrees Celsius.
 2. The system of claim 1,wherein said power and refrigeration cascade system is grid-independent.3. The system of claim 1, wherein the refrigeration system is thermallycoupled to said load powered by the electric power system, and whereinthe refrigeration system is operable to match cooling demands of theload.
 4. The system of claim 1, wherein the absorption system is drivenby waste heat from the electric power system.
 5. The system of claim 1,wherein the thermal coupling between the refrigeration system and theabsorption system enables a refrigeration system condensing temperatureof less than approximately fifteen degrees Celsius.
 6. The system ofclaim 1, wherein the electric power system is selected from the groupconsisting of a heat-engine-driven electric generator and a fuel cell.7. The system of claim 1, wherein the electric power system deliverselectricity, wherein said electricity is selected from the groupconsisting of direct current (DC) and alternating current (AC)electricity.
 8. The system of claim 1, wherein the refrigeration systemis selected from the group consisting of a vapor compression system, areversed Brayton system, a reversed Stirling system, a thermoelectricsystem, and a magneto-caloric system.
 9. The system of claim 1, whereinthe absorption system is selected from the group consisting of awater-cooled absorption system and an air-cooled absorption system. 10.The system of claim 1, wherein the absorption system is selected fromthe group consisting of a single-effect absorption system and amultiple-effect absorption system.
 11. The system of claim 1, whereinthe absorption system has an evaporator temperature of less thanapproximately twenty degrees Celsius.
 12. The system of claim 1, whereinthe absorption system has an evaporator temperature in the range ofapproximately five to ten degrees Celsius.
 13. The system of claim 1,wherein the refrigeration system is thermally coupled to said loadpowered by the electric power system, and wherein said load comprises adata center.
 14. The system of claim 13, wherein the refrigerationsystem is operable to cool said data center.
 15. The system of claim 14,wherein the electric power system provides direct current (DC) power tosaid data center.
 16. The system of claim 1, wherein the refrigerationsystem is thermally coupled to said load powered by the electric powersystem, and wherein said load comprises an air conditioning system. 17.The system of claim 1, wherein the refrigeration system is thermallycoupled to said load powered by the electric power system, and whereinsaid load comprises a supermarket cooler.
 18. The system of claim 1,wherein the refrigeration system is thermally coupled to said loadpowered by the electric power system, and wherein said load comprises adisplay case.
 19. An on-site power generation system, comprising: anelectric power system; and a refrigeration cascade system thermallycoupled to the electric power system, wherein the refrigeration cascadesystem is configured to temporally match cooling needs of a load coupledto the electric power system based on actual power supplied to the load.20. A refrigeration cascade system, comprising: a) a refrigerationsystem configured: i) to be powered at least in part by electricity; andii) to be thermally coupled to a load powered by electricity; and b) anabsorption system thermally coupled to the refrigeration system andconfigured to remove heat rejected by the refrigeration system, whereinthe thermal coupling between the refrigeration system and the absorptionsystem enables a refrigeration system condensing temperature and anabsorption system evaporating temperature which are within less thanapproximately ten degrees Celsius of each other.
 21. The refrigerationcascade system of claim 20, wherein said absorption system is driven bywaste heat from an electric power system.
 22. A datacenter power andcooling system, comprising: an electric power system; at least oneserver rack powered by the electric power system; a refrigeration systempowered at least in part by the electric power system and thermallycoupled to the at least one server rack for removing heat from the atleast one server rack; and an absorption system thermally coupled to therefrigeration system and configured to remove heat rejected by therefrigeration system, wherein the thermal coupling between therefrigeration system and the absorption system enables a refrigerationsystem condensing temperature of less than approximately twenty degreesCelsius.
 23. The datacenter power and cooling system of claim 22,wherein the electric power system is selected from the group consistingof a direct current (DC) and an alternating current (AC) electric powersystem.
 24. The datacenter power and cooling system of claim 22, whereinthe absorption system is driven by waste heat from the electric powersystem.
 25. The datacenter power and cooling system of claim 22, whereinthe thermal coupling between the refrigeration system and the absorptionsystem enables a refrigeration system condensing temperature of lessthan approximately fifteen degrees Celsius.
 26. The system of claim 22,further comprising a plurality of server racks, and wherein therefrigeration system comprises a plurality of vapor compression systems,one for each server rack.
 27. The datacenter power and cooling system ofclaim 24, further comprising a plurality of server racks, wherein eachserver rack is cooled by a separate refrigeration system comprising acondenser, wherein said condensers are cooled by chilled liquid from theabsorption system.
 28. A method of reducing energy consumption by acomputer chip powered by a power source, comprising: thermally couplingthe computer chip to a refrigeration system; powering the refrigerationsystem at least in part by the power source; thermally coupling therefrigeration system to an absorption system, wherein the thermalcoupling between the refrigeration system and the absorption systemenables a refrigeration system condensing temperature and an absorptionsystem evaporating temperature which are within less than approximatelyten degrees Celsius of each other.
 29. The method of claim 28, whereinthe absorption system is driven by waste heat from the power source. 30.The method of claim 28, wherein the power source is selected from thegroup consisting of at least one fuel cell and at least one combustionengine.
 31. The method of claim 28, wherein the power source comprisesan on-site power source.
 32. The method of claim 31, wherein the on-sitepower source comprises a direct current (DC) power source.
 33. Themethod of claim 32, wherein the direct current (DC) power sourcecomprises at least one fuel cell.
 34. The method of claim 28, whereinthe computer chip comprises CMOS technology.
 35. The method of claim 28,wherein the computer chip is located in a datacenter server rack.